Merge pull request #113 from growthbook/fix/leak-ios18.5

**Root Cause:** Retain cycle in `FeaturesViewModel.connectBackgroundSync()`:
- `SSEHandler.onDisconnect` closure was capturing `streamingUpdate` strongly
- Created circular reference preventing proper deallocation
- iOS 18.5's stricter memory management caught this issue

Author: madhuchavva

Sources/CommonMain/Features/FeaturesViewModel.swift

@@ -16,6 +16,8 @@ class FeaturesViewModel {
     var encryptionKey: String?
     /// Caching Manager
     let manager: CachingLayer
+    /// SSE Handler for background sync
+    internal var sseHandler: SSEHandler?
 
     init(delegate: FeaturesFlowDelegate, dataSource: FeaturesDataSource, cachingManager: CachingLayer) {
         self.delegate = delegate
@@ -26,20 +28,30 @@ class FeaturesViewModel {
 
     func connectBackgroundSync(sseUrl: String) {
         guard let url = URL(string: sseUrl) else { return }
+        
+        // Disconnect existing connection if any
+        sseHandler?.disconnect()
+        
         let streamingUpdate = SSEHandler(url: url)
+        sseHandler = streamingUpdate
+        
         streamingUpdate.addEventListener(event: "features") { [weak self] id, event, data in
             guard let jsonData = data?.data(using: .utf8) else { return }
             self?.prepareFeaturesData(data: jsonData)
         }
         streamingUpdate.connect()
 
-        streamingUpdate.onDissconnect { _, shouldReconnect, _ in
+        streamingUpdate.onDissconnect { [weak streamingUpdate] _, shouldReconnect, _ in
             if let shouldReconnect = shouldReconnect, shouldReconnect {
-                streamingUpdate.connect()
+                streamingUpdate?.connect()
             }
         }
     }
 
+    deinit {
+        sseHandler?.disconnect()
+    }
+    
     private func fetchCachedFeatures(logging: Bool = false) {
         // Check for cache data
         if let data = manager.getContent(fileName: Constants.featureCache) {